Field of the Invention
The present invention relates to an automatic transmission for a vehicle. More particularly, the present invention relates to a planetary gear train for an automatic transmission of a vehicle that improves power delivery performance and fuel efficiency as a consequence of achieving eleven forward speed stages using a minimum number of constituent elements, enlarging a span of shift ratios, and almost linearly increasing or decreasing step ratios between transmission steps.
Description of Related Art
In recent years, a rise in oil price has caused unlimited competition for enhancing fuel efficiency.
As a result, researches into reduction of weight and enhancement of the fuel efficiency through down-sizing are being conducted in the case of an engine and researches for simultaneously securing operability and fuel efficiency competitiveness through multistages are conducted in the case of an automatic transmission.
However, in the automatic transmission, as a number of transmission steps increases, the number of internal components increases, and as a result, mountability, cost, weight, transmission efficiency, and the like may still deteriorate.
Accordingly, development of a planetary gear train which may bring about maximum efficiency with a small number of components may be important in order to increase a fuel efficiency enhancement effect through the multistages.
In this aspect, in recent years, 8-speed automated transmissions have tended to be achieved and the research and development of a planetary gear train capable of implementing more transmission steps have also been actively conducted.
Since a span of shift ratios of the recent 8-speed automatic transmission is merely 6.5 to 7.5, the 8-speed automatic transmission has no great effect of improving fuel efficiency.
In addition, since step ratios between transmission step may not be increased or decreased linearly in a case in which a span of shift ratios of the 8-speed automatic transmission is greater than or equal to 9.0, driving efficiency of an engine and drivability of a vehicle may be deteriorated. Accordingly, there is a need for development of a highly efficient automatic transmission with 9 or more forward speed stages.
The information disclosed in this Background of the Invention section is only for enhancement of understanding of the general background of the invention and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art already known to a person skilled in the art.